The present invention relates to digital video signal recording apparatus and, more particularly, to a digital video tape recorder (VTR) which is suited for commercial or professional use.
In digital video tape recorders designed for commercial use, video and audio signals are respectively digitized and then recorded in separate areas of a recording track. It is known to operate a digital VTR in a so-called after-recording mode in which an audio signal, for example, is recorded on a recording track on which a video signal has previously been recorded.
It is also known in a digital VTR to perform so-called multi-track recording in which signals are distributed among a plurality of channels for simultaneous recording or reproduction by a plurality of heads. For multi-track recording digital VTRs, it has been proposed to fabricate a plurality of heads together in a single head unit in order to simplify assembly and reduce the number of adjustments required for proper alignment of the heads. However, when after-recording is effected by a digital video tape recorder having a plurality of heads fabricated together in a head unit, the level of the recording signal is very high as compared with that of a reproduced signal so that a video signal reproduced by one head may be disturbed by cross-talk from an audio signal that is simultaneously being after-recorded by another head of the head unit. In this case it may be that a satisfactory reproduced picture cannot be obtained.
FIGS. 1A-1D of the accompanying drawings show tracks A and B which are recorded on, and reproduced from, a tape T by heads a and b, respectively. As shown in FIGS. 1A-1D, on each of the tracks A and B, there are provided a recording area AT1 in which a first tracking adjustment signal is recorded, a first auxiliary recording area AU1 in which a first audio signal is recorded, a second auxiliary recording area AU2 in which a second audio signal is recorded, a recording area VI in which a video signal is recorded, a recording area SC in which a sub code is recorded and a recording area AT2 in which a second tracking adjustment signal is recorded. The respective areas are formed sequentially in the order stated above starting at the beginning of the track and proceeding in the head scanning direction (i.e., from left to right in FIGS. 1A-1D). In order to simplify the drawings, only the respective recording areas of track A are labelled.
The formation of the respective recording areas comes about as a result of the provision of the various types of recording signals to the recording head at times when the head is scanning the respective areas.
FIG. 1A shows the positions of heads a and b relative to the recording areas at a time when leading head a is beginning the after-recording of the first audio signal in recording area AU1 of track A.
Fig. 1B shows the positions of the heads at a time when head a is completing the after-recording of the first audio signal in recording area AU1 of track A.
FIG. 1C shows the positions of the heads when trailing head b is beginning the after-recording of the first audio signal in recording area AU1 of track B.
FIG. 1D shows the positions of the heads when trailing head b is completing the after-recording of the first audio signal in recording area AU1 of track B.
It will be observed that, at the time shown in FIG. 1D, the playback by leading head a of the video signal recorded in recording area VI of the track A has already started. Consequently, cross-talk from the audio signal being recorded by the trailing head b occurs so that the video signal reproduced by head a is disturbed during a period in which head a scans the hatched portion of recording area VI of track A.
To overcome this problem, it has been proposed to mask the reproduced video signal during the period of the disturbance so that the deteriorated portion of the picture is not displayed. According to this previously-proposed method, however, a complete reproduced picture is not provided in the after-recording mode. Furthermore, in digital video tape recorders in which shuffling of video signal data is used, it is frequently observed that a masking of some of the video signal causes deterioration in the entire picture.
In copending U.S. patent application Serial No. 07/852,729, filed Mar. 17, 1992, which has an inventor in common with the present application and which is commonly assigned with this application, the recording areas in each track are arranged so that a video signal recording area precedes audio signal recording areas, and adjacent tracks are offset by a step distance in the head scanning direction. It is proposed in this copending application that a pair of heads be mounted on a head base so that the heads are displaced from each other in the head scanning direction by a distance that is less than the sum of the step distance and the length of a gap between the video recording area and the following audio recording area. The purpose of this arrangement is to prevent disturbance of the video signal during after-recording of an audio signal.